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From "David Jencks (JIRA)" <jetspeed-...@portals.apache.org>
Subject [jira] Created: (JS2-457) JetspeedPipeline synchronization is broken and using a threadlocal is really ugly
Date Thu, 29 Dec 2005 03:16:02 GMT
JetspeedPipeline synchronization is broken and using a threadlocal is really ugly

         Key: JS2-457
         URL: http://issues.apache.org/jira/browse/JS2-457
     Project: Jetspeed 2
        Type: Bug
  Components: Container  
    Reporter: David Jencks

I previously addressed these issues in J2-115 and still think that is a better solution. 
Here is a way to remove use of a threadlocal to track a call's progress through the valves
that does not change any classes or configuration other than JetspeedPipeline.

In addition, the synchronization in JetspeedPipeline is fairly useless.  Some problems include:

suppose 2 calls come simultaneously and block on valves1.  The first call changes valves to
point to valves2.  While the second call is changing valves2 to valves3, while locking valves1,
a third call comes in, finds valves2 unlocked, and changes valves2 to vavles4.  The result
might be valves3 or valves4, but won't have both changes.

Also, the access to valves while traversing the pipeline needs to be synchronized, or there
is no guarantee that a completely written vavle array will be accessed: according to arguments
made around "double checked locking is broken", the JIT can rearrange code so that the "valves"
variable can be set before the array is filled in.

I believe all the synchronization can be removed if the addValve and removeValve methods are
eliminated.   I personally think this would be a good idea.

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